1. Field
The embodiments described below relate generally to the delivery of therapeutic radiation to a patient. More specifically, some embodiments are directed to the delivery of radiation therapy to moving target volumes.
2. Description
According to conventional radiation therapy, a beam of radiation is directed toward a target volume (e.g., a cancerous tumor) located within a patient. The radiation beam delivers a predetermined dose of therapeutic radiation to the target volume according to an established treatment plan. The delivered radiation kills cells of the target volume by causing ionizations within the cells or other radiation-induced cell damage.
Treatment plans for delivering radiation to a patient are intended to maximize radiation delivered to a target volume, while minimizing the radiation delivered to healthy tissue. However, due to respiration and other involuntary patient motion, a target volume may move and/or change shape while a patient is positioned to receive a treatment beam.
One conventional method for delivery of radiation treatment to a moving target includes using an irradiation field that is large enough to account for target excursions from a nominal position. This method places surrounding healthy tissue or organs at an increased risk of also receiving radiation. Gated treatment involves determining a window of time during which the target movement is minimal, and to deliver a treatment beam to the target only during that window of time. Gated treatment presents an inefficient use of resources due to the significant time periods during which a treatment beam is not delivered.
Yet another proposed technique for delivering a treatment beam to a moving target uses an auxiliary device to determine the location and the shape of the target at any point in time and to continuously reshape the leaves of an MLC (multi-leaf collimator) to follow (i.e., track) the determined location and shape. However, this technique requires a dynamically-controllable (i.e., velocity and position control) collimator and sophisticated imaging and registration systems. Even so equipped, systems employing this technique have difficulty attaining desired levels of precision.
Systems are needed for delivering therapeutic radiation to moving target volumes which provide an improved treatment duty cycle (and thereby increased treatment speed), suitable accuracy, and/or simplified operation.